520H P220 onan cylinder head leak??

[oe espo 32]

Is it possible to have a leaking head gasket and still have 90 psi compression cold?? 

 

Got this this 520 recently. Didn't run .  I put an ignition control module and got it to run. Smokes when startup. Also smokes a little. Adjusted valves when I tried to get it running. Pressure washed it and it seems that there is black condensation coming at the back cylinder head gasket area. I guess air from flywheel comes out there? But I thought was a blown gasket, looked like it was puffing. Compression seems adequate  to me. Front cylinder is also 90. New plugs are black as coal already.

 

Any suggestions?? Valve job? I don't think manual recommends it.

Not sure if should put new gaskets on?

New ew valve seals while I'm at it. Never had one apart but looks like motor has to be pulled. Any suggestions appreciated. Also sometimes no voltage when trying to start. Battery terminals clean.

[ericj 1,576]

could the float in the carb be set wrong causing the motor to run rich. i think the service manual tell you how to adj

 

 

 

eric j

[km3h 543]

Did you remove the heads when you adjusted the valves? Onan recommends that you remove heads and decarbonise the engine every 500 hours. Did you remove the engine tins and clean the area under them. Almost impossible to do unless you remove the engine from the tractor. But I guarantee you that you will be glad to do it after you see all the junk packed between the cooling fins. Heat is the biggest factor in a breakdown of the rear cylinder on these engines.  

[oe espo 32]

I removed the tins and cleaned when I pulled the flywheel to change the ign control module. It was pretty rough. Cleaned by hand didn't pressure wash. I didn't take the heads off when I adjusted the valves because I didn't think I would have good access to the rear head. 1,156 hours not sure if its still ticking or not?

 

How big of a job to pull the motor? Should I lift it out or just rotate it 90 degrees??

[ericj 1,576]

disconnect the 9 pin providing its not butchered up disconnect the fuel line.throttle, choke cables, and 4 bolts that hold the motor to the mounting plate and wal-la you can pull the motor or rotate it what ever is easier for you. the onan motor with a good 9 pin are very easy to change

 

 

 

eric j 

 

 

 

 

sorry i forgot you have to remove the pto clutch and the pto hoop and twist the motor a little to get the drive belt off

Edited November 23, 2014 by ericj

[oe espo 32]

Aha thanks. I see the first problem. 9 pin eliminated by PO  any suggestions?  Should I try to reestablish an OEM 9 pin?

 

[ericj 1,576]

i redo all of my 9 pins if for no other reason then for the ease of interchange ability of motor between my tractor. when you have as many onans as i do it helps. i can swap motors if i need or desire to do so. not sure how many i will do but i have swapped motor around @ time for one reason or another. but it also helps when doing service on them and trouble shooting them electrically

 

 

 

 

eric j  

[oe espo 32]

I suppose you can still get the connectors OEM style

[ericj 1,576]

check with martin he replaced his i get mine from a friend who orders them on line but not sure were he gets them

 

 

 

 

eric j

[oe espo 32]

Ok ill look for the connectors. In the meantime I pulled the tins except for the muffler can't get the screws out. Here is a picture of what I suspect is a blown or leaking head gasket. The black area that looks wet.

Where I'm baffled is the 90 psi on both cylinders. I hear that is adequate?

[boovuc 1,090]

On the Onan, 90 PSI is adequate but don't expect a lot more hours from the engine with 90 PSI on both cylinders. I would crimp in a new 9 pin connector and pull that motor to replace the gaskets and decarbon each cylinder. If you adjusted the valves recently, they should be OK. There are "how to" threads with tips on how to remove the carbon from these engines. 

[oe espo 32]

Can I re-ring to get the compression or is that a wasted teardown?

[ericj 1,576]

a lot of times when people change the oil they don't clean up after words and the flywheel throws the oil around and causes the motor to cake up and over heat eventually so i would recommend that you pull the tins and clean thoroughly i just use simple green or purple power wish i had a pressure washer

 

 

 

 

 

eric j   

[km3h 543]

Don't cross bridges until you come to them. These engines are rebuilt every day and hold up very well. Get the heads off and get rid of the carbon. If the cylinder walls are not scored, You might want to put new rings in there but if you decide not to I don't think you will have trouble.   

[oe espo 32]

Haven't looked up head bolt torque yet but some were almost finger tight. Standard bore. Seemed like a lot of oil on bottom of cylinder. Intake valve is pretty carboned up on stem. Not sure if this is normal or a concern.  What do you guys think of the scoring. Two on each cylinder catch a fingernail

[km3h 543]

The carbon is normal and should be cleaned. Scoring is never a good thing but a lot depends on how bad it is. Would cross hatching it and a new set of rings fix it?  

[rick 215]

Clean the carbon out, adjust the valves, use OEM parts to put back together and run with it. Champion RS17YX plugs are the latest recommendation. Use GOOD fuel, I use 89 octane Shell and 3 ounces of Shaeffer Neutra to 5 gallons gas. Top tier fuel goes a long way to reducing deposits in the engine.

[Theroundhousernr 589]

   I think 90 psi is the bottom end of the spectrum for compression on that onan. Mine read between 110 and 115 psi. Important thing is they  seemed to have aged evenly together.

 

  If you want a good worker, re ring if its even an option depending on cylinder/piston wear or rebuild.

 

  If you just want to put around. Set the valves, clean carbon, clean carb, and have fun.

[oe espo 32]

Looking at the carbon buildup and how fun it is to clean up.  I'm going to try the better fuel option.  It didn't cross my mind that pool fuel a contributor to the carbon  I had the valves ground but a local guy, He say they were pretty good.  I plan to lap them in, put new seals in and put back together.  starting to snow here.  i have no real history of the motor so once i get it up and running we will see how it runs and how much oil it uses.  if it gulps it then ill plan for an expensive rebuild.  appreciated everyone's input for newbie like me.

[ericj 1,576]

onan says compression can vary between 75 and 115 psi  for an acceptable motor. if you adjust the valves recheck your compression. and something i learn is that you check compression on an onan with the throttle and choke open. it make a difference sometimes 

 

 

 

 

eric j

[JackC 616]

"I plan to lap them in"  That is not recommended for these engines although it should not be a major problem.  The seats should be 45 degrees and the valves 44 degrees.  

 

Best to read the service manual when working on the ONANs.  For example when servicing the valves:

 

IMPORTANT: Do not lap valves. The sharp seating

surface between the valve and seat will

be removed resulting in shorter valve

life.

 

16. If valve faces are worn, burned or pitted, grind

valves to a 44 degree face angle (A) following

manufacturers instructions. If valve face margin ( is

less than 0.787 mm (0.031 in.) after grinding, replace

valve.

[oe espo 32]

I had the valves ground, then re-ground to the on an spec. Shop thought they are all the same.  All buttoned back up. Test fired about 4 times.  Tightened everything back up put all the tins back on and guess what. That B@%$T^ won't start.  Ready to scream.  Fuel like crazy plugs are fuel fouled.  Pulled plug, Checked for spark got spark.  Inline spark tester still got spark.  I have no idea where to start now.

[ericj 1,576]

test the coil i had a hard starting onan and it turned out to be the coil. it would start a little hard normal but almost not start at all the colder it got. if the coil checks out ok then you have to look at the carb. i had a p216 that i couldn't get to start at an idle or run but would at above half throttle, i swapped  out the carb and it ran fine good luck

 

 

 

 

 

eric j

[oe espo 32]

The coil is new and ignition control module is new.  I just bought it last year non-running.  I was so excited to get 520! The joy has worn off fixing all the PO issues.  Fuel is pulsing good.  The non-running issue was a sheared flywheel key and bad ign control module   what is bothering me is that I fired up several times no problem before I put all the tin on and buttoned up the cable rounting. Any suggestion appreciated. Thanks everyone. 

[546cowboy 301]

Since you have 90 p.s.i. compression, you have spark on both cylinders and you are getting fuel to the carb, then I would say you have a carb problem. Since you say the plugs are black it is obviously flooding and if it floods when you are trying to start it then it will not start with the wet plugs.

 

Just remove the top of the carb and clean out the bowl, I fill the bowl with carb cleaner that you can soak a carb in, put the top back on and let it sit overnight,  then I clean that out and blow out all the passages with air.

 

I would also check the voltage at the red wire on the coil while you are cranking the engine. If the voltage drops to 9 volts or less you have a battery or connector problem.

 

I also only use 91 octane gas in all my Horses and add Stabil to all my gas for my equipment because that gas sits there for quite awhile before it gets used when you are not mowing every three or four days.

Edited February 11, 2015 by 546cowboy